Metabolic acclimation of tetraploid and hexaploid wheats by cold stress-induced carbohydrate accumulation

Metabolic acclimation of plants to cold stress may be of great importance for their growth, survival and crop productivity. The accumulation carbohydrates associated with cold tolerance (CT), transcript levels for genes encoding related enzymes along with damage indices were comparatively studied in three genotypes of bread and durum wheats differing in sensitivity. Two (Norstar, bread wheat and Gerdish, durum wheat) were tolerant and the other, SRN (durum wheat), was susceptible to cold stress. During cold stress (-5°C for 24h), the contents of electrolyte leakage index (ELI) in Norstar and then Gerdish plants were lower than that of SRN plants, particularly in cold acclimated (CA) plants (4°C for 14days), confirming lethal temperature 50 (LT₅₀) under field conditions. Increased carbohydrate abundances in the cases of sucrose, glucose, fructose, hexose phosphates, fructan, raffinose, arabinose resulted in different intensities of oxidative stress in bread (Norstar) plants compared to durum plants (SRN and Gerdish) plants as well as in CA plants compared to non-acclimated (NA) ones under cold, indicating metabolic/regulatory capacity along with a decrease in ELI content and enhanced defense activities. A significant decrease in these carbohydrates, particularly sucrose, under cold in NA plants showed an elevated level of cell damage (confirmed by ELI) compared to CA plants. On the other hand, an increase in hexose phosphates, particularly in NA plants, indicated sucrose degradation along with greater production of glucose and fructose compared to CA plants. Under such conditions, a significant increase in transcript levels of sucrose synthase and acidic invertase confirmed these results. Under cold, the high ABA-containing genotypes like Norstar and then Gerdish, which were obvious in CA plants, partly induced relative acclimation of cells for acquisition of CT compared to SRN. These results reveal an important role of carbohydrate metabolism in creating CT in durum wheats (particularly in Gerdish) as well as bread wheat with possible responsive components in metabolic and transcript levels.